The present invention relates generally to improvements to an actuator design and more particularly to improvements in an actuator design for use in automotive applications.
It will be recognized that a solenoid assembly can be used in various actuator assemblies for actuation of a certain component and not limited to motor vehicles or internal combustion engines. One use for an actuator assembly having a linear solenoid involves a vehicle evaporative system.
Most motor vehicles are now equipped with a carbon canister installed to trap and store petroleum fuel vapors from the carburetor bowl and/or the fuel tank. Through the use of the canister, fuel vapors are not vented to the atmosphere, but are instead trapped in the canister and then periodically purged from the canister into the engine where they are burned along with the air-fuel mixture. A solenoid valve assembly is typically used to control purging of the carbon canister as well as diverting the flow of other gases within the system.
The solenoid valve assembly includes a plunger that is movable between an open position, wherein the outlet port is not blocked and purge air communicates with the carbon canister, and a closed position, wherein the outlet port is blocked. When a coil of a solenoid within the valve assembly is energized, the magnetic force of the coil will manipulate the position of the plunger and move it to an open position. The solenoid valve for this type of valve assembly will stay open as long as the coil is energized.
Existing solenoid mechanisms include a spring installed in compression within the plunger to bias the plunger in a closed position. When the coil within the cylindrical solenoid mechanism is de-energized, the spring returns the plunger to the closed position wherein a valve cap is pressed tightly against a valve seat thereby blocking the flow of fluids through the valve assembly. The solenoid valve will remain closed as long as the coil remains de-energized.
Different flow rates or purge strategies may be utilized to achieve the desirable purge performance for an engine or other applications of the valve assembly (e.g. limiting or controlling flow between a supply (reservoir) and destination. Some applications require high flow rates with a fully open valve, while others require low flow rates to maximize the control at a low purge ratio.
Existing solenoid mechanisms are fundamentally of linear proportional behavior which means that the output is controlled by means of controlling the armature""s displacement or position with the input signal (percent duty cycle). Thus, the slope of the flow of the fuel vapors versus percent duty cycle function of the solenoid mechanism is constant. Such linear proportional purge has in some cases not provided enough resolution to operate at engine idle conditions. As such, there is a need to have a higher flow resolution at lower duty cycles and also provide high flow rates regardless of the low resolution at larger duty cycle values. Accordingly, it is desired that operation of the solenoid mechanism is fully stable at a wide range of vehicle underhood operating conditions using an electrical input signal driver to control the displacement of the armature.
In an exemplary embodiment, a method for controlling a plunger of a magnetic actuator assembly is disclosed. The method includes: generating a first magnetic flux at the plunger; biasing the plunger by means of the first magnetic flux opposing a first bias from a first spring having a first spring rate; disposing a second spring in series communication with the first spring, the second spring having a second spring rate, such that a combined spring rate of the first and second springs in series is less than either of the first and second spring rates; generating a second magnetic flux at the plunger; and biasing the plunger by means of the second magnetic flux higher than the first magnetic flux opposing a second bias from the first and second springs in series communication.
In another embodiment, a magnetic actuator assembly is disclosed. The magnetic actuator assembly includes: an armature plunger in operable communication with an actuator of the magnetic actuator; a coil configured to generate a first magnetic flux at the plunger; a first spring having a first spring rate in operable communication with the plunger biased by means of the first magnetic flux opposing a first bias from the first spring; and a second spring in series communication with the first spring, the second spring having a second spring rate, such that a combined spring rate of the first and second springs in series is less than either of the first and second spring rates, wherein when the coil is further energized to generate a second magnetic flux higher than the first magnetic flux, the plunger is biased opposing a second bias from the first spring and the second spring in series communication.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following brief description of the drawings.